Francis, PaulHewett, Paul C.Foltz, Craig B.Chaffee, Frederic H.2018-09-112018-09-110004-637Xhttp://hdl.handle.net/1885/147320The classification of QSO rest-frame optical and UV spectra is undertaken by means of a statistical principal component analysis (PCA) emphasizing the relation between QSO properties. The PCA is applied directly to a sample of QSO UV spectra from the Large Bright QSO Survey, and relations are studied between continuum, emission-line, and broad-absorption-line properties. Quantitative classifications are derived based on a limited number of principal components, and three components account for approximately 75 percent of the sample and describe: emission-line core strength, continuum slope, and broad absorption features. Broad-absorption-line QSOs appear as a natural subclass of the population with characteristic excess emissions, and continuum hardness correlates with the equivalent widths of C IV and Lyman-alpha emission lines. Quantitative properties are derived from the study that serve to classify QSO emissions ranging from broad low-equivalent-width lines to narrow high-equivalent-width lines.application/pdfhttp://www.sherpa.ac.uk/romeo/issn/0004-637X/..."Publisher's version/PDF may be used on any website or authors' institutional repository" from SHERPA/RoMEO site (as at 11/09/18).199210.1086/171870